The importance of amino acid transport and metabolism in the nervous system is well recognized. Of special significance is glutamic acid which lies at the center of nitrogen metabolism and is the most abundant amino acid in the nervous system. Histochemical studies have shown that the glutamic acid moiety of glutathione is transferred to an acceptor amino acid or oligopeptide at two specialized sites in the nervous system, i.e. the brush border of the choroid plexus and the capillary endothelium of the blood brain barrier. The transfer reaction is catalyzed by gamma-glutamyl transpeptidase (gamma-glutamyl transferase E.C.2.3.2.2.) which not only degrades glutathione, but also may be operative in the translocation of a variety of amino acids across cell surfaces. At present, factors controlling the levels and catalytic activity of the gamma-glutamyl transpeptidase are unknown. In addition, firm evidence establishing the role of the gamma-glutamyl transpeptidase in amino acid translocation is lacking but several pieces of information are suggestive. We propose to study the kinetic and physical properties of purified gamma-glutamyl transpeptidase in order to identify the regulatory mechanisms which govern the catalytic activity of this enzyme in the nervous system. We also plan to isolate brush border membranes from choroid plexus in order to study the function of gamma-glutamyl transpeptidase in the translocation of amino acids across cellular surfaces.